Investigators in New York City were left with a range of questions Tuesday after a driver plowed a pickup truck onto a bike path and into a crowd in Lower Manhattan, killing at least eight people and injuring 11.

The suspect, identified as Sayfullo Saipov, 29, is originally from Uzbekistan and is not a U.S. citizen. Fox reports.

The attack on a bright Halloween afternoon occurred not far from the new World Trade Center building and the site of the attacks of Sept. 11, 2001.

Saipov had handwritten notes pledging his loyalty to the Islamic State terror network and shouted “Allahu akbar” (“God is great”) after the crash, law enforcement officials told Fox News.

Saipov, who was shot by police, was taken into custody and remained hospitalized.

The suspect had a green card, a source told Fox News. Saipov came to the U.S. in 2010, and, according to the Associated Press, has a Florida driver’s license but was said to be living in Paterson, N.J.

Saipov was an Uber driver who had passed a background check, the company told Fox News. It added that Saipov has now been banned from the app, and Uber has offered assistance to the FBI.

Saipov’s notes, written in Arabic and pledging loyalty to ISIS, turned up in and near the vehicle, Fox News was told. In addition, the New York Post reported that investigators found “an image of the ISIS flag inside his vehicle.”

Four of the injured were teachers and students who were riding on a short yellow school bus near Stuyvesant High School when they were hit by the suspect’s Home Depot rental truck. One student remained in critical condition.

A victim killed in the attack was a Belgian citizen, Belgian Deputy Prime Minister and Foreign Affairs Minister Didier Reyners tweeted Tuesday. Three Belgians were also injured.

Others killed in the attack were Argentine citizens, according to Argentina’s Foreign Ministry. Argentine newspaper La Nacion reported five of the eight people killed were Argentines traveling in the U.S. on a celebratory vacation.

Those killed, according to the country’s Ministry of Foreign Affairs, were Hernán Mendoza, Diego Angelini, Alejandro Pagnucco, Ariel Erlij and Hernán Ferruchi.

The attack was being treated as an act of terrorism. At a news conference Tuesday evening, New York City Mayor Bill de Blasio called the attack “an act of terror and a particularly cowardly act of terror aimed at innocent civilians.”

New York Gov. Andrew Cuomo described it as a “lone wolf” attack, and added that there was no immediate evidence to suggest that there was a wider plot.